[Compositor threaded scrollbar scrolling] Animate Mac track click.

This CL fixes an issue with Mac scrollbars which caused scrollbar
track clicks to not get animated.

Bug: 1025147
Change-Id: I7304cb8e9a6c02439ee7c4a6e7f6c1d3dbfeebf2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917956
Commit-Queue: Rahul Arakeri <arakeri@microsoft.com>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716909}

ui/events/blink/input_handler_proxy.cc

@@ -708,12 +708,18 @@ void InputHandlerProxy::RecordMainThreadScrollingReasons(
   }
 }
 
-bool InputHandlerProxy::ShouldAnimate(bool has_precise_scroll_deltas) const {
+bool InputHandlerProxy::ShouldAnimate(blink::WebGestureDevice device,
+                                      bool has_precise_scroll_deltas) const {
+  if (!smooth_scroll_enabled_)
+    return false;
+
 #if defined(OS_MACOSX)
   // Mac does not smooth scroll wheel events (crbug.com/574283).
-  return false;
+  return device == blink::WebGestureDevice::kScrollbar
+             ? !has_precise_scroll_deltas
+             : false;
 #else
-  return smooth_scroll_enabled_ && !has_precise_scroll_deltas;
+  return !has_precise_scroll_deltas;
 #endif
 }
 
@@ -794,8 +800,9 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollBegin(
     scroll_status = input_handler_->RootScrollBegin(
         &scroll_state, GestureScrollInputType(gesture_event.SourceDevice()));
   } else if (ShouldAnimate(
+                 gesture_event.SourceDevice(),
                  gesture_event.data.scroll_begin.delta_hint_units !=
-                 ui::input_types::ScrollGranularity::kScrollByPixel)) {
+                     ui::input_types::ScrollGranularity::kScrollByPixel)) {
     DCHECK(!scroll_state.is_in_inertial_phase());
     scroll_status = input_handler_->ScrollAnimatedBegin(&scroll_state);
   } else {
@@ -863,8 +870,9 @@ InputHandlerProxy::HandleGestureScrollUpdate(
   in_inertial_scrolling_ = scroll_state.is_in_inertial_phase();
   gfx::PointF scroll_point(gesture_event.PositionInWidget());
 
-  if (ShouldAnimate(gesture_event.data.scroll_update.delta_units !=
-                    ui::input_types::ScrollGranularity::kScrollByPixel)) {
+  if (ShouldAnimate(gesture_event.SourceDevice(),
+                    gesture_event.data.scroll_update.delta_units !=
+                        ui::input_types::ScrollGranularity::kScrollByPixel)) {
     DCHECK(!scroll_state.is_in_inertial_phase());
     base::TimeTicks event_time = gesture_event.TimeStamp();
     base::TimeDelta delay = base::TimeTicks::Now() - event_time;

ui/events/blink/input_handler_proxy.h

@@ -168,7 +168,8 @@ class InputHandlerProxy : public cc::InputHandlerClient,
                         const cc::InputHandlerScrollResult& scroll_result);
 
   // Whether to use a smooth scroll animation for this event.
-  bool ShouldAnimate(bool has_precise_scroll_deltas) const;
+  bool ShouldAnimate(blink::WebGestureDevice device,
+                     bool has_precise_scroll_deltas) const;
 
   // Update the elastic overscroll controller with |gesture_event|.
   void HandleScrollElasticityOverscroll(

ui/events/blink/input_handler_proxy_unittest.cc

@@ -743,6 +743,71 @@ TEST_P(InputHandlerProxyTest, GestureScrollIgnored) {
   VERIFY_AND_RESET_MOCKS();
 }
 
+TEST_P(InputHandlerProxyTest, AnimatedScrollbarScroll) {
+  VERIFY_AND_RESET_MOCKS();
+  SetSmoothScrollEnabled(true);
+  expected_disposition_ = InputHandlerProxy::DID_HANDLE;
+  gesture_.SetSourceDevice(blink::WebGestureDevice::kScrollbar);
+  gesture_.data.scroll_begin.delta_hint_units =
+      gesture_.data.scroll_update.delta_units =
+          ui::input_types::ScrollGranularity::kScrollByPixel;
+
+  // Test setup for a kGestureScrollBegin.
+  gesture_.SetType(WebInputEvent::kGestureScrollBegin);
+  EXPECT_CALL(mock_input_handler_, ScrollAnimatedBegin(_))
+      .WillOnce(testing::Return(kImplThreadScrollState));
+  EXPECT_EQ(expected_disposition_,
+            input_handler_->RouteToTypeSpecificHandler(gesture_));
+  EXPECT_TRUE(input_handler_->gesture_scroll_on_impl_thread_for_testing());
+
+  VERIFY_AND_RESET_MOCKS();
+
+  // Test setup for a kGestureScrollUpdate.
+  gesture_.SetType(WebInputEvent::kGestureScrollUpdate);
+  EXPECT_CALL(mock_input_handler_, ScrollAnimated(_, _, _))
+      .WillOnce(testing::Return(kImplThreadScrollState));
+  EXPECT_EQ(expected_disposition_,
+            input_handler_->RouteToTypeSpecificHandler(gesture_));
+  EXPECT_TRUE(input_handler_->gesture_scroll_on_impl_thread_for_testing());
+
+  VERIFY_AND_RESET_MOCKS();
+}
+
+TEST_P(InputHandlerProxyTest, NonAnimatedScrollbarScroll) {
+  VERIFY_AND_RESET_MOCKS();
+  SetSmoothScrollEnabled(false);
+  expected_disposition_ = InputHandlerProxy::DID_HANDLE;
+  gesture_.SetSourceDevice(blink::WebGestureDevice::kScrollbar);
+  gesture_.data.scroll_begin.delta_hint_units =
+      gesture_.data.scroll_update.delta_units =
+          ui::input_types::ScrollGranularity::kScrollByPixel;
+
+  // Test setup for a kGestureScrollBegin.
+  gesture_.SetType(WebInputEvent::kGestureScrollBegin);
+  EXPECT_CALL(mock_input_handler_, ScrollBegin(_, _))
+      .WillOnce(testing::Return(kImplThreadScrollState));
+  EXPECT_EQ(expected_disposition_,
+            input_handler_->RouteToTypeSpecificHandler(gesture_));
+  EXPECT_TRUE(input_handler_->gesture_scroll_on_impl_thread_for_testing());
+
+  VERIFY_AND_RESET_MOCKS();
+
+  // Test setup for a kGestureScrollUpdate.
+  gesture_.SetType(WebInputEvent::kGestureScrollUpdate);
+  gesture_.data.scroll_update.delta_y =
+      -40;  // -ve value implies "scrolling down".
+  EXPECT_CALL(
+      mock_input_handler_,
+      ScrollBy(testing::Property(&cc::ScrollState::delta_y, testing::Gt(0))))
+      .WillOnce(testing::Return(scroll_result_did_scroll_));
+  EXPECT_CALL(mock_input_handler_, ScrollAnimated(_, _, _)).Times(0);
+  EXPECT_EQ(expected_disposition_,
+            input_handler_->RouteToTypeSpecificHandler(gesture_));
+  EXPECT_TRUE(input_handler_->gesture_scroll_on_impl_thread_for_testing());
+
+  VERIFY_AND_RESET_MOCKS();
+}
+
 TEST_P(InputHandlerProxyTest, GestureScrollByPage) {
   // We should send all events to the widget for this gesture.
   expected_disposition_ = InputHandlerProxy::DID_NOT_HANDLE;